JPG vs PNG: which should you use?

Two properties decide this, and everything else follows from them: JPG throws detail away and cannot store transparency; PNG keeps every pixel and can.

Use JPG when

• It is a photograph, and file size matters at all.
• There is no transparency to preserve.
• It is going somewhere that must accept the most universally-supported format — an old system, a print shop's upload form, a legacy CMS.

Use PNG when

• The image contains text, a logo, a diagram, a screenshot or line art.
• You need a transparent background.
• It is a working file you will edit and re-save more than once.

What goes wrong when you pick wrong

A screenshot saved as JPG gets a grey-brown fringe around every letter, because the hard edges of text are exactly the high-frequency detail JPEG discards first. It also usually ends up larger than the PNG would have been — the worst of both outcomes.

A photograph saved as PNG is often five to ten times the size of the equivalent JPG, with no visible benefit, because there is almost no exact repetition in a photograph for lossless compression to exploit.

Converting a transparent PNG to JPG flattens the transparency onto a solid background. Dexta's Convert Format asks which colour to use; the transparency itself is gone from the output and cannot be recovered.

What Dexta supports

JPG, PNG and WebP work as both input and output. GIF and BMP can be read, but they come back out as PNG. HEIC from an iPhone and camera RAW files are not supported at all — browsers cannot reliably decode them, so convert those on the device first.

Mistakes worth avoiding

• Converting JPG to PNG to "improve quality". It cannot restore what JPEG already discarded — you get a bigger file containing the same damage.
• Round-tripping between formats repeatedly. Every trip through JPG loses more.
• Using PNG for photographs on a web page. It is the single most common cause of a slow-loading page.